The subject matter disclosed herein relates to the art of rotary wing aircraft and, more specifically, to coaxial multi-rotor systems for rotary wing aircraft.
In typical rotary winged aircraft, for example, helicopters with dual coaxial rotor systems, rotary power is transmitted from an engine through a gearbox into the rotor system. The gearbox transfers power to a lower rotor shaft to drive a lower rotor assembly and to an upper rotor shaft coaxial with the lower rotor shaft to drive the upper rotor assembly. The systems typically include several sets of bearings between the upper rotor shaft and lower rotor shaft to transfer loads between the shafts and to the housings. The bearings and controls for the upper rotor assembly drive an increased diameter for the upper rotor shaft, and thus the lower rotor shaft, which increases drag during operation. As such, many coaxial rotor systems include an aerodynamic fairing positioned between the upper rotor assembly and the lower rotor assembly. Typical systems attach to the upper and lower rotor shafts and include a significant derotation mechanism to prevent the fairing from rotating with respect to the airframe, and to keep the fairing oriented in a selected direction.
In one embodiment, a coaxial, dual rotor system connected to a gearbox includes a first rotor assembly is located at a rotor axis and which imparts a first axial load and a first moment and a first rotor shaft operably connected to the first rotor assembly at the rotor axis to drive rotation of the first rotor assembly about the rotor axis. A first bearing assembly connects the gearbox to the first rotor shaft and transfers the first axial load from the first rotor shaft to the gearbox. A second rotor assembly is located at the rotor axis and imparts a second axial load and a second moment. A second rotor shaft is operably connected to the second rotor assembly at the rotor axis to drive rotation of the second rotor assembly about the rotor axis, the second rotor shaft coaxial with and radially offset from the first rotor shaft. A second bearing assembly connects the gearbox to the second rotor shaft and transfers the second axial load from the second rotor shaft to the gearbox. A nonrotating standpipe is located at the rotor axis radially between the first rotor shaft and the second rotor shaft. An intershaft bearing assembly is located at the standpipe and transfers the first and second moments from the first rotor assembly and the second rotor assembly to the standpipe using the first and second bearing assemblies.
In another embodiment, a dual coaxial rotor rotorcraft includes an airframe and a drive system including a gearbox located at the airframe. A dual coaxial rotor system is operably connected to the drive system. The rotor system includes a first rotor assembly is located at a rotor axis and which imparts a first axial load and a first moment and a first rotor shaft operably connected to the first rotor assembly at the rotor axis to drive rotation of the first rotor assembly about the rotor axis. A first bearing assembly connects the gearbox to the first rotor shaft and transfers the first axial load from the first rotor shaft to the gearbox. A second rotor assembly is located at the rotor axis and imparts a second axial load and a second moment. A second rotor shaft is operably connected to the second rotor assembly at the rotor axis to drive rotation of the second rotor assembly about the rotor axis, the second rotor shaft coaxial with and radially offset from the first rotor shaft. A second bearing assembly connects the gearbox to the second rotor shaft and transfers the second axial load from the second rotor shaft to the gearbox. A nonrotating standpipe is located at the rotor axis radially between the first rotor shaft and the second rotor shaft. An intershaft bearing assembly is located at the standpipe and transfers the first and second moments from the first rotor assembly and the second rotor assembly to the standpipe using the first and second bearing assemblies. These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.